The present invention relates to a multilayer tube shoulder for a tube and to a method for the manufacture of such tube shoulders according to the preambles of the independent claims.
The prior art discloses numerous tube shoulders for tubes. Currently, such tube shoulders are almost exclusively made from thermoplastic material by injection molding and are then welded to the tubular tube body in a further operation.
Certain plastics, such as polyethylene (PE), have a considerable permeability for oxygen, carbon dioxide and odorous/aromatizing substances. In the case of tube shoulders made from these materials, undesired substances diffuse or pass out of the tube into the environment or pass from the environment into the tube, which is prejudicial to the substance introduced into the tube. In order to prevent this harmful permeability, tube shoulders generally have a two-layer structure, comprising an outer, shaping layer and an inner barrier layer.
The material generally used for the shaping layer is polyethylene (PE), while the barrier layer material is polyethylene terephthalate (PET). The fact that these materials do not adhere to one another constitutes one of the main problems in the rational, economic manufacture of tube shoulders.
The use of multilayer tube shoulders of PE and PET has been adopted. Thus, the prior art discloses numerous attempts to rationally and economically manufacture known, multilayer tube shoulders. U.S. Pat. No. 4,185,757 discloses one such attempt. However, none of the known solutions is completely satisfactory. Since tube shoulders are mass produced articles, the price is mainly determined by two factors: cost/material consumption and cycle time for manufacture. The tube shoulders known from the prior art on the one hand have an excessive material consumption, which has a negative effect on the consumption of resources, and therefore costs and environmental compatibility. On the other hand they cannot be manufactured rationally, because they require long cycle times. In fact, certain tube shoulders even require several injection molds and several operations, which amounts to a poor utilization of the machines and molds.
The problem of non-mutually adhering materials has in the prior art led to inefficient or even impracticable solutions. As e.g. in U.S. Pat. No. 4,185,757, these are based on filigree undercuts and keys or wedges, which are intended to bring about a positive connection between the inner barrier layer and the outer, shaping layer of a tube shoulder. These undercuts and keys e.g. comprise mutually corresponding grooves and ribs, which are generally made at right angles to the symmetry axis of the tube shoulder and are so constructed that they must be forcibly demolded.
Another multilayer tube shoulder is described in European patent application EP-130 239. This application teaches a multilayer tube shoulder having an inner barrier layer adhering by friction to an outer, shaping layer. This arrangement is unsatisfactory for various reasons. Firstly, the two layers must be combined in a separate operation. Secondly, there is no reliable hold between the two parts. Thirdly, the parts require increased manufacturing precision, which, inter alia, takes into account the differing shrinkage behavior of the materials.
The parts of the above-described tube shoulders can generally only be further processed after complete cooling. It is also necessary to manually join the individual parts in a separate operation. Thus, the prior art arrangements lead to the manufacturing process for the corresponding tube shoulders being directly and completely decelerated.
The present invention is directed toward a tube shoulder and method for making a tube shoulder that avoids the disadvantages discussed in conjunction with the aforementioned prior art. On the one hand, by means of the present invention, drastic material reductions are possible and, on the other hand, the manufacturing time is greatly reduced and optimized, leading to a better utilization of the invested resources.
Compared with the prior art the invention has two vital advantages. On the one hand the material consumption of a two-layer tube shoulder is massively reduced and on the other the cycle time during manufacture is drastically decreased.
The invention disclosed here is also suitable for integrally joining a tube body to the tube shoulder in a first step. This tube body can be supplied as an extraneous part from the outside to the processing operation. This additional step advantageously takes place in a further cavity or is combined with one of the steps in which the first or second material component is produced.